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Implement PR1786 by iterating between dead cycle elimination
and simplifycfg in the rare cases when it is needed. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44044 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
41fcea3bdb
commit
b42c8f7101
@ -27,6 +27,7 @@
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Pass.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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@ -50,9 +51,9 @@ FunctionPass *llvm::createCFGSimplificationPass() {
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}
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static bool MarkAliveBlocks(BasicBlock *BB,
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SmallPtrSet<BasicBlock*, 16> &Reachable) {
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SmallPtrSet<BasicBlock*, 128> &Reachable) {
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std::vector<BasicBlock*> Worklist;
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SmallVector<BasicBlock*, 128> Worklist;
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Worklist.push_back(BB);
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bool Changed = false;
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while (!Worklist.empty()) {
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@ -93,42 +94,46 @@ static bool MarkAliveBlocks(BasicBlock *BB,
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return Changed;
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}
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// It is possible that we may require multiple passes over the code to fully
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// simplify the CFG.
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//
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bool CFGSimplifyPass::runOnFunction(Function &F) {
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SmallPtrSet<BasicBlock*, 16> Reachable;
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/// RemoveUnreachableBlocks - Remove blocks that are not reachable, even if they
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/// are in a dead cycle. Return true if a change was made, false otherwise.
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static bool RemoveUnreachableBlocks(Function &F) {
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SmallPtrSet<BasicBlock*, 128> Reachable;
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bool Changed = MarkAliveBlocks(F.begin(), Reachable);
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// If there are unreachable blocks in the CFG...
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if (Reachable.size() != F.size()) {
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assert(Reachable.size() < F.size());
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NumSimpl += F.size()-Reachable.size();
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// Loop over all of the basic blocks that are not reachable, dropping all of
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// their internal references...
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for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB)
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if (!Reachable.count(BB)) {
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI!=SE; ++SI)
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if (Reachable.count(*SI))
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(*SI)->removePredecessor(BB);
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BB->dropAllReferences();
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}
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for (Function::iterator I = ++F.begin(); I != F.end();)
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if (!Reachable.count(I))
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I = F.getBasicBlockList().erase(I);
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else
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++I;
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Changed = true;
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}
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if (Reachable.size() == F.size())
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return Changed;
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assert(Reachable.size() < F.size());
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NumSimpl += F.size()-Reachable.size();
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// Loop over all of the basic blocks that are not reachable, dropping all of
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// their internal references...
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for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB)
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if (!Reachable.count(BB)) {
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI!=SE; ++SI)
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if (Reachable.count(*SI))
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(*SI)->removePredecessor(BB);
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BB->dropAllReferences();
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}
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for (Function::iterator I = ++F.begin(); I != F.end();)
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if (!Reachable.count(I))
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I = F.getBasicBlockList().erase(I);
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else
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++I;
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return true;
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}
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/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
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/// iterating until no more changes are made.
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static bool IterativeSimplifyCFG(Function &F) {
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bool Changed = false;
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bool LocalChange = true;
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while (LocalChange) {
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LocalChange = false;
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// Loop over all of the basic blocks (except the first one) and remove them
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// if they are unneeded...
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//
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@ -140,6 +145,31 @@ bool CFGSimplifyPass::runOnFunction(Function &F) {
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}
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Changed |= LocalChange;
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}
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return Changed;
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}
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// It is possible that we may require multiple passes over the code to fully
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// simplify the CFG.
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//
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bool CFGSimplifyPass::runOnFunction(Function &F) {
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bool EverChanged = RemoveUnreachableBlocks(F);
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EverChanged |= IterativeSimplifyCFG(F);
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// If neither pass changed anything, we're done.
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if (!EverChanged) return false;
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// IterativeSimplifyCFG can (rarely) make some loops dead. If this happens,
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// RemoveUnreachableBlocks is needed to nuke them, which means we should
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// iterate between the two optimizations. We structure the code like this to
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// avoid reruning IterativeSimplifyCFG if the second pass of
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// RemoveUnreachableBlocks doesn't do anything.
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if (!RemoveUnreachableBlocks(F))
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return true;
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do {
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EverChanged = IterativeSimplifyCFG(F);
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EverChanged |= RemoveUnreachableBlocks(F);
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} while (EverChanged);
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return true;
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}
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100
test/Transforms/SimplifyCFG/iterative-simplify.ll
Normal file
100
test/Transforms/SimplifyCFG/iterative-simplify.ll
Normal file
@ -0,0 +1,100 @@
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; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | not grep bb17
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; PR1786
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define i32 @main() {
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entry:
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%retval = alloca i32, align 4 ; <i32*> [#uses=1]
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%i = alloca i32, align 4 ; <i32*> [#uses=7]
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%z = alloca i32, align 4 ; <i32*> [#uses=4]
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%z16 = alloca i32, align 4 ; <i32*> [#uses=4]
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%"alloca point" = bitcast i32 0 to i32 ; <i32> [#uses=0]
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store i32 0, i32* %i
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%toBool = icmp ne i8 1, 0 ; <i1> [#uses=1]
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br i1 %toBool, label %cond_true, label %cond_false
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cond_true: ; preds = %entry
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store i32 0, i32* %z
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br label %bb
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bb: ; preds = %cond_next, %cond_true
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%tmp = load i32* %z ; <i32> [#uses=1]
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%tmp1 = sub i32 %tmp, 16384 ; <i32> [#uses=1]
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store i32 %tmp1, i32* %z
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%tmp2 = load i32* %i ; <i32> [#uses=1]
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%tmp3 = add i32 %tmp2, 1 ; <i32> [#uses=1]
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store i32 %tmp3, i32* %i
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%tmp4 = load i32* %i ; <i32> [#uses=1]
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%tmp5 = icmp sgt i32 %tmp4, 262144 ; <i1> [#uses=1]
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%tmp56 = zext i1 %tmp5 to i8 ; <i8> [#uses=1]
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%toBool7 = icmp ne i8 %tmp56, 0 ; <i1> [#uses=1]
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br i1 %toBool7, label %cond_true8, label %cond_next
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cond_true8: ; preds = %bb
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call void @abort( )
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unreachable
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cond_next: ; preds = %bb
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%tmp9 = load i32* %z ; <i32> [#uses=1]
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%tmp10 = icmp ne i32 %tmp9, 0 ; <i1> [#uses=1]
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%tmp1011 = zext i1 %tmp10 to i8 ; <i8> [#uses=1]
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%toBool12 = icmp ne i8 %tmp1011, 0 ; <i1> [#uses=1]
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br i1 %toBool12, label %bb, label %bb13
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bb13: ; preds = %cond_next
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call void @exit( i32 0 )
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unreachable
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cond_false: ; preds = %entry
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%toBool14 = icmp ne i8 1, 0 ; <i1> [#uses=1]
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br i1 %toBool14, label %cond_true15, label %cond_false33
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cond_true15: ; preds = %cond_false
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store i32 0, i32* %z16
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br label %bb17
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bb17: ; preds = %cond_next27, %cond_true15
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%tmp18 = load i32* %z16 ; <i32> [#uses=1]
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%tmp19 = sub i32 %tmp18, 16384 ; <i32> [#uses=1]
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store i32 %tmp19, i32* %z16
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%tmp20 = load i32* %i ; <i32> [#uses=1]
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%tmp21 = add i32 %tmp20, 1 ; <i32> [#uses=1]
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store i32 %tmp21, i32* %i
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%tmp22 = load i32* %i ; <i32> [#uses=1]
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%tmp23 = icmp sgt i32 %tmp22, 262144 ; <i1> [#uses=1]
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%tmp2324 = zext i1 %tmp23 to i8 ; <i8> [#uses=1]
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%toBool25 = icmp ne i8 %tmp2324, 0 ; <i1> [#uses=1]
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br i1 %toBool25, label %cond_true26, label %cond_next27
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cond_true26: ; preds = %bb17
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call void @abort( )
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unreachable
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cond_next27: ; preds = %bb17
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%tmp28 = load i32* %z16 ; <i32> [#uses=1]
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%tmp29 = icmp ne i32 %tmp28, 0 ; <i1> [#uses=1]
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%tmp2930 = zext i1 %tmp29 to i8 ; <i8> [#uses=1]
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%toBool31 = icmp ne i8 %tmp2930, 0 ; <i1> [#uses=1]
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br i1 %toBool31, label %bb17, label %bb32
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bb32: ; preds = %cond_next27
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call void @exit( i32 0 )
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unreachable
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cond_false33: ; preds = %cond_false
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call void @exit( i32 0 )
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unreachable
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cond_next34: ; No predecessors!
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br label %cond_next35
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cond_next35: ; preds = %cond_next34
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br label %return
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return: ; preds = %cond_next35
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%retval36 = load i32* %retval ; <i32> [#uses=1]
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ret i32 %retval36
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}
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declare void @abort()
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declare void @exit(i32)
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